1. Technical Field
The present invention relates to a die mounting substrate and a method of fabricating the same.
2. Description of the Related Art
With the recent reduction in size and fabrication cost of electronic apparatuses, electronic components such as semiconductor chips or packages for molding the semiconductor chips, including BGA, CSP, WLP and so on, are surface-mounted on a mounting substrate by a flip chip bonding process using a solder base material (solder ball).
However, the flip chip bonding process using solder balls is difficult to apply when a mounting substrate has the same size as that of an electronic component. In particular, in the case where soldering is performed using a typical solder paste having an average particle size of 5˜20 μm, solder balls have a diameter of 105˜120 μm, undesirably making it difficult to cope with fineness of a circuit pattern. Also, because solder balls subjected to reflow have a spherical shape, the adhesion area of the solder balls to the circuit pattern is reduced, undesirably weakening an interfacial adhesion force and bringing adjacent solder balls into contact with each other. As well, in order to solve problems with reliability resulting from different coefficients of thermal expansion between the mounting substrate and the electronic component, shear stress should be relieved at the connection portions. In the case where the height of solder balls is increased, shear stress at the connection portions may be relieved. However, limitations are imposed on increasing the height of solder balls which use a solder base material.
With the goal of solving the above problems, there have been proposed methods of forming copper pillars on the mounting substrate or electronic component through plating and photolithography and then printing solder balls thereon, but the plating and photolithography increase the process costs and are complicated, undesirably lowering the process yield.
In addition, although attempts to use a double solder ball structure are being made, problems of interfacial adhesion force of the solder balls to the circuit pattern being reduced due to fineness of the circuit pattern and of adjacent solder balls coming into contact with each other still occur.